I am almost sure that that is what is forming the foam in the pool. (please e-mail me if you think I am wrong)

a bit of water is running down the filter around the screws. small tinny airbubles seem to go in the pool they are continuous and seem to be the guilty party that is forming the thin cover of foam that is covering the surface of my pool.

I have a spare filter that I think I could take the gasket from (are they interchangeable, not sure)

How can I be sure that it is the gasket and if it is, how do I change.

if you are talking about the o ring that seals the multiport valve to the filter body,you might try this with filter running and you are seeing the bubbles out the returns start pouring water slowly around the bottom of the valve where the o ring seals, the idea is if the gasket,or o ring is bad it will start sucking in the water you are pouring instead of air. if the bubbles stop during this test ,the o ring is probably bad.

Well Grandma, what is your calcium hardness level? Soft water will foam much easier than hard. Aeration can make it worse. If your water is full or organics from lack of shocking and you also have soft water you can get a lot more foaming. Add in certain algaecides and it can really get interesting. And of course there are swim suits that are not rinsed enough and add soap. God forbid you get dish soap in there or the foam will get several feet high. And air leaks will make any foaming worse than what it would be without it.

The air itself will usually come from the suction side. Possibly low water will create a small whirlpool in your skimmer and sucks a small amount of air in constantly.